I followed the instructions. Went to System Preferences, added everything and I have a Flag at the top of my screen which I can click to give me US, Romaji, Hiragan and Katakana.
I would like to enter for example Biru where the "I" is long.
I select the Romaji keyboard but I do not know how to enter the long "I" vowel. Is this possible? Right now it seems like the US keyboard and the Romaji keyboard selections act just the same.